1. Field of the Invention
The present invention relates to a method and apparatus for sticking a polarizer to a substrate and, more particularly, to a method and apparatus for sticking a polarizer to a substrate such as a liquid crystal panel with an adhesive layer while peeling a separate sheet.
2. Prior Art
Generally, a liquid crystal panel is formed by sealing a liquid crystal material in a space in a liquid crystal cell formed between facing surfaces of two glass substrates and may include sticking a polarizer to an outer surface of each of the two glass substrates in the liquid crystal panel.
The polarizer has a stacked structure in which a polarizing film for polarizing light is used as a base material, one of surfaces of the polarizer is covered with a protection film, and an adhesive layer applied on the other surface is protected by a separate sheet.
In a process of manufacturing a liquid crystal panel, the polarizer is stuck to the liquid crystal panel by peeling the separate sheet on the polarizer to expose the adhesive layer and sticking the polarizer to an outer surface of the glass substrate with the exposed adhesive layer.
When the work of sticking the polarizer to the liquid crystal panel is performed manually, the work efficiency is extremely low, and variations occur in the finished product. Consequently, an apparatus for automatically sticking a polarizer to a liquid crystal panel has already been proposed.
A conventional apparatus for automatically performing the sticking operation has at least two stages, a liquid crystal panel receiving mechanism and an sticking mechanism. A table reciprocates between the two stages to stick the polarizer to the liquid crystal panel while peeling the separate sheet.
A work process in the conventional sticking apparatus having such a configuration includes the following steps.
(1) In the liquid crystal panel receiving mechanism, the liquid crystal panel is set on the table and is simultaneously positioned.
(2) The table comes to a predetermined position in the sticking mechanism.
(3) A polarizer is supplied onto an adhesive belt of the sticking mechanism and is adhered on an adhesive surface of the adhesive belt.
(4) By feeding the adhesive belt, the polarizer is guided by a wedge-shaped guide member and moves obliquely while a separate sheet is peeled by using a guide roller as a base point.
(5) The tip of the polarizer from which the separate sheet is being peeled is pressed against the top surface of the liquid crystal panel by a press roller and the table is moved back, thereby sticking the polarizer onto the liquid crystal panel.
(6) The liquid crystal panel on which the polarizer is stuck is taken from the table (refer to, for example, Japanese Unexamined Patent Publication No. 8-50290).
As another conventional apparatus for performing automatic sticking, an apparatus having a table on which a liquid crystal panel is vacuum held and a table on which a polarizer is vacuum held is proposed. The tables are moved among a supply stage, a separate sheet peeling stage, a sticking stage, and the like, and a sticking process is automatically carried out (refer to, for example, Japanese Unexamined Patent Publication No. 2002-23151).
In the former conventional apparatus, the polarizer is stuck to the liquid crystal panel while the table moves between the two stages, so that an install space which is twice as large as the size of the liquid crystal panel or the polarizer is necessary. Consequently, the apparatus has a problem such that it is not suitable for sticking a polarizer to a large liquid crystal panel.
A large liquid crystal panel here denotes a panel having a size of 25 inches or larger. For example, a liquid crystal panel of 45 inches has a length of about 1000 mm and a width of about 600 mm. A polarizer to be stuck to such a large liquid crystal panel also has the same size. In the former conventional apparatus, therefore, an extremely wide install space has to be assured.
Since the polarizer is stuck to the liquid crystal panel by reciprocating the table and the work of removing the liquid crystal panel to which the polarizer is stuck from the table is necessary, the work efficiency of the polarizer sticking process is very low.
Further, at the time of sticking the polarizer and the liquid crystal panel, as shown in FIG. 2 of Patent Japanese Unexamined Publication No. 8-50290, a wedge-shaped guide member is interposed between the liquid crystal panel and the polarizer.
As understood from FIG. 2 of Publication No. 8-50290, a considerably large space is necessary between the liquid crystal panel and the tip of the polarizer.
This is because it is limited to thin the guide member, a guide roller for peeling a separate film is provided at the tip of the guide member and, further, a space to prevent the adhesive surface of the adhesive belt from coming into contact with the liquid crystal panel is necessary.
In a state where such a large space is provided, when a press roller is lowered to press the polarizer against the top surface of the liquid crystal panel, the polarizer having even a large angle is pressed against the liquid crystal panel.
As a result, the portion against which the polarizer is pressed is largely curved (distorted) and is damaged. In addition, a characteristic change may occur and the function of the polarizer itself may deteriorate. Moreover, when the space between the liquid crystal panel and the polarizer is large, air bubbles and the like tend to enter at the time of sticking, and it may cause poor sticking.
The polarizer is constructed so as to move on the guide member by the feed travel of the adhesive belt in a state where the polarizer is adhered by the adhesive belt using an adhesive tape such as Scotch tape.
It is important to stick the liquid crystal panel and the polarizer while maintaining the accurately positioned state.
In the conventional apparatus, however, the polarizer is simply held by being adhered by the adhesive belt of the material such as Scotch tape. The polarizer is moved by travel of the adhesive belt. Moreover, the separate film is peeled at the tip of the guide member, and the tip portion of the polarizer is pressed so as to be stuck to the liquid crystal panel. Consequently, even a slight deviation from the intended path of travel of the adhesive belt causes a positional deviation in the polarizer. As a result, an adverse influence is exerted on sticking precision. Particularly, in the case of a large polarizer, there is limitation in such a moving method.
In the conventional apparatus as described above, the adverse influence on sticking precision is not the only problem. Since the polarizer and the liquid crystal panel in the sticking end portion are apart from each other, just before the end of sticking, the end portion of the polarizer suffers warping. It causes poor sticking due to air bubbles.
Further, for the same reasons, the latter conventional apparatus is also not suitable for sticking of a polarizer to a large liquid crystal panel and also has a problem of low work efficiency.